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ISWI remodelers slide nucleosomes with coordinated multi-base-pair entry steps and single-base-pair exit steps
Sebastian Deindl1, William L Hwang, Swetansu K Hota
1Howard Hughes Medical Institute, Harvard University, Cambridge, MA 02138, USA.
Cell
|February 5, 2013
Summary
ISWI-family remodelers use a coordinated mechanism to slide nucleosomes along DNA. This chromatin remodeling process involves precise 1 bp DNA translocations toward the exit side before multi-base pair movements on the entry side.
Area of Science:
- Molecular Biology
- Biochemistry
- Epigenetics
Background:
- ISWI-family enzymes are crucial for chromatin remodeling, facilitating nucleosome sliding along DNA.
- The precise molecular mechanism of nucleosome translocation by these enzymes remains largely undetermined.
Purpose of the Study:
- To elucidate the step-by-step mechanism of nucleosome translocation employed by ISWI-family remodelers.
- To investigate the coordination between DNA movement at the entry and exit sides of the nucleosome.
Main Methods:
- Utilized single-molecule Förster Resonance Energy Transfer (smFRET) to monitor nucleosome translocation dynamics.
- Analyzed the stepping patterns and DNA movement during the remodeling process.
Main Results:
- Identified a conserved stepping pattern across different ISWI-family members, driven by the catalytic subunit.
- Demonstrated that nucleosome remodeling initiates with a 7 bp exit-side DNA translocation, followed by 3 bp steps, all composed of 1 bp substeps.
- Observed that entry-side DNA translocation occurs only after significant exit-side movement, with each entry step enabling further exit-side translocation.
Conclusions:
- Proposed a detailed remodeling mechanism involving highly coordinated, sequential DNA translocations at distinct nucleosomal sites.
- Highlighted a mechanism where 1 bp exit-side translocations precede multi-base pair movements on the entry side, ensuring efficient chromatin remodeling.
